In the field of telecommunications, conventional copper wires are being largely replaced by transmission lines employing optical fibres. It is necessary in this case, in which optical rather than electrical signals are transmitted, to provide a distribution and organizing facility for the fibre-optic cables at appropriate locations within exchanges inside telecommunication companies, office buildings or in curb side facilities. These so-called distribution frames or distributors group together a plurality of termination or access points on the optical network, which allow the connection of devices or customers to various services provided on the network, as well as between them. A typical distributor consists of several cable heads, which are structures for actually mounting optical connection modules, optical devices and which also contain means for cable handling such as individualisers.
In this respect, and due to the sheer number of connections, it is useful, if the connection of new customers or devices or the modification of existing connections is possible without disturbing the other existing connections provided in the cable head. To that end, cable heads are generally built in a modular way, comprising a plurality of optical connection modules and also optical devices.
Each optical connection module serves the purpose of connecting optical fibres of a main cable (the so-called network cable) and/or of distribution cables (station cables) to cables running to the customer or optical device, or they may also serve for interconnecting optical fibres of distribution cables. Often, the modules also contain storage space for spare length of optical fibre in order to be able to cut (cleave) and reconnect connections between optical fibres at a later stage. It is necessary to provide such spare lengths because on one hand fibre length is lost during the cleaving process, and on the other hand the new cable end to be connected may be positioned at a greater distance from where the original connection took place.
Optical devices, on the other hand, perform functions within the network such as splitting (passive optical device) or amplification (active optical device). The cable head thus generally comprises a housing and cassettes supported by the housing for stowing optical fibres and fibre splices, or optical devices.
Optical modules of the mentioned type are, for example disclosed in U.S. Pat. No. 5,093,885. These comprise a housing, a connector panel and splicing trays inserted behind the connector panel into the housing. The connector panel is pivotally mounted on the housing, and can be opened to allow access to the rear of the connectors as well as to the splicing trays. Upon installation, the network or station cable is passed into the housing, is individualised and fixed to the splicing trays, where they are spliced to intermediate fibres leading to the connector panel. Cables from customers or optical devices are then connected to the connector panel by suitable connectors, such as pigtails.
EP 0 538 164 discloses, for example, a distribution head for fibre-optic cables, which employs a modular system for housing optical connection modules. It comprises a plurality of splicing organizers and a connection support plate fixed in separate places but in proximity to each other on the same drawer-like support, which is mounted in a pivoting way on the distribution head housing. Thereby it is possible to pivotally rotate the support out of the housing into an open position and perform installation and maintenance tasks. The splicing organizers can themselves be opened individually and receive partly individualized fibre-optic cables from the main network, which are spliced within them to intermediate fibres leading out to the connection support plate, where fibre-optic cables from devices or customers are attached via connectors, for example pigtails, to the intermediate fibres.
While this arrangement allows to some extent for individual handling of connections without disturbing other existing ones, the necessity to pivot the whole support carrying several splicing organizers and the connection support plate makes it unsuitable for locations where space is restricted. Also, in order to access an individual fibre or connection, it is necessary to move all optical fibres mounted in the cable head, and displace one or more splicing organizers, installation or maintenance work thereby being more time-consuming and error-prone.
A more space efficient solution is provided by U.S. Pat. No. 5,740,299 in which instead of having splicing organizers and connectors pivoted out together on a single support base, individual cassettes are pivotally supported by routing members, which in turn are connected together to form an aligned stack-like assembly. The incoming and outgoing network or station cables, or cables from optical devices are fed through the routing members to the individual cassettes, in which their optical fibres are spliced together and any excess length is stored.
In this case the cassettes do not provide connectors such as pigtails, rather connections have to be made by splicing within each pivotable cassette, and both incoming and outgoing fibres enter the cassette via the same passages in the routing member and via an attached flexible conduit necessary to protect the fibres against damage by excessive bending. This means that due to the space saving nature of the assembly both establishing and modifying connections from the network or station to customers or devices, or between the latter, requires considerable time and effort, and has to be performed in relatively little space.